Hydromechanical transmission

ABSTRACT

A power transmission. Two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, each providing an input member, an output member, and a reaction member. The input member of one gear train is connected to an input means, and the two input members of the two gear trains are interconnected so that both are driven by the input means. The reaction members of the two gear trains are also interconnected. The output members of the two gear trains are separately clutchable to an output means, and speed varying means cause one output member to increase its speed and simultaneously cause the other output member to decrease its speed, and vice versa. The speed varying means may comprise a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, one of the units being connected in driving relation to the input means, and the other being connected in driving relation to the reaction members.

[ 1 HYDROMECHANIC AL TRANSMISSION Elias Orshansky, .lr., San Francisco, Calif.

[73] Assignee: Orshansky Transmission Corporation, New York, NY.

[22] Filed: Sept. 25, 1972 [21] Appl. No.1 291,803

Related US. Application Data [63] Continuation-impart of Ser. No. 259,549, June 5, 1972, which is a continuation-in-part of Ser. No. 154,976, June 21, I971, abandoned.

[75] inventor:

[52] U.S. Cl 74/687; 74/681 [51] Int. Cl. F1611 47/04 [58] Field of Search r. 74/687, 681, 686, 688, 74/689, 690

[56] References Cited UNITED STATES PATENTS 2,504,040 4/1950 Orshansky, Jr. .1 74/687 X 2,580,946 1/1952 Orshansky, Jr. 74/687 2,931,250 4/1960 Ebert .1 74/687 3,079,813 3/1963 Quigley 74/687 3,455,183 7/1969 Orshansky, Jr. 74/687 3,596,535 8/1971 Polak H 74/687 X 3,675,507 7/1972 Takekawa 74/687 [4 1 June 10, 1975 Primary Examiner-Samuel Scott Assistant Examiner.lohn Reep Attorney, Agent, or Firm-Owen, Wickersham & Erickson [57] ABSTRACT A power transmission. Two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, each providing an input member, an output member, and a reaction member. The input member of one gear train is connected to an input means, and the two input members of the two gear trains are interconnected so that both are driven by the input means. The reaction members of the two gear trains are also interconnected. The output members of the two gear trains are separately clutchable to an output means, and speed varying means cause one output member to increase its speed and simultaneously cause the other output member to decrease its speed, and vice versa. The speed varying means may comprise a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa. one of the units being connected in driving relation to the input means, and the other being connected in driving relation to the reaction members.

49 Claims, 16 Drawing Figures PATENTEDJUH I 0 I975 FIG.

INVENTOR. ELIAS ORSI-IANSKY, JR.

ATTORNEYS PATENTEUJUNIO I975 3.888.139

saw 2 FIG. 2

1 NTOR ELIAS ORSHANS JR.

ATTORNEYS PATENTEIJJUH 10 ms 3,888,139

SHLET 5 FIG. 5

INVENTOR. ELIAS ORSHANSKY, JR.

ATTORNEYS PATENTEDJUH 10 m5 SHEET vmm vmm

ROM

mZOmc-m SHEET PATENTEIJJUH 1 0 I975 mimvl m? @I SHEET PATENTEDJUH 10 ms mimvl 1 HYDROMECHANICAL TRANSMISSION CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 259,549 filed June 5, 1972, which was a continuation-in-part of application Ser. No. l54,976 filed June 21, 1971, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a hydromechanical infinitely variable transmission. It provides for improved utilization of vehicle engine power by enabling the engine to operate within a narrow speed range which has been optimized for minimum emissions, maximum fuel economy and maximum power, regardless of vehicle operating conditions.

When utilizing conventional torque converter or manual transmission, many compromises are imposed upon the engine because it must provide adequate performance over a wide range of torque and speed. The practice of most vehicle manufactures of providing a selection of optional axle ratios for the vehicle is only one of the many attempts which have been made to reduce the compromise for any given application.

With an infinitely variable transmission, the engine can always be operated in a speed range in which it is capable of producing rated power. Therefore, vehicle performance in any given application can be maintained or even improved while utilizing a smaller engine. However, infinitely variable transmissions of the pure hydrostatic type are limited to applications where significant power losses can be tolerated in return for the benefits of improved transmission ratio control.

Hydromechanical transmisions offer the control benefits of a hydrostatic transmission, and, since only a portion of the engine power is transmitted by the hydraulic units, they provide a means of removing the performance barrier of excessive power losses. The extent to which any hydromechanical transmission can accomplish this is a function of the percentage of power which must be transmitted hydraulically.

The transmission of this invention can transmit high horsepower over a wide range of output speed variation at a constant input speed and horsepower. It is a plane tary-hydraulic device which differs from the previous transmissions in its ability to transmit power over a wide range with a minimum of transmitted hydraulic horsepower, and a minimum of installed hydraulic horsepower. It provides full engine braking over its entire range of operation.

The invention avoids the pitfalls of excessive complexity, speeds or loads in the gear train. Maximum reliability and minimum cost have been obtained by utilizing standard commercial hydraulic units which are operated totally within their long-life rated conditions of speed and power. In addition, the clutches can utilize the same low'cost paper elements presently employed in high production automobile torque converter transmissions. For a comparable power rating, a smaller number of elements than in a torque converter power shift transmission can be utilized, because at all shift points the clutch elements are virtually synchronous. The number of elements is, therefore, a function not of their thermal capacity, but of their steadystate torque capacity.

Among the fields of applications of the transmission of this invention are passenger and competition cars,

highway and off-highway trucks, buses, agricultural and construction equipment, military vehicles, and industrial drives and machine tools.

The invention makes it possible to design transmissions of an extremely wide range of speed and torque variation at full power. This is required in construction and off-highway equipment, for example, where torque multiplication of the order of l8:l and 24:1 may be encountered. Machine tool drives may require even wider ranges, and they are possible.

The use of this transmission in a piston engine vehicle enables reduction of exhaust emissions and improvement in the specific fuel consumption by programming the engine to operate within its optimum range under all road conditions without regard to transmission torque output requirements. Both the NOx and CH emissions can be minimized by optimizing the engine for operation in a specific narrow range. In addition, a smaller engine may be utilized for any application, as the transmission enables full engine power to be developed at any vehicle speed except for the lower speeds where the vehicle is traction limited. It is particularly desirable to operate turbocharged diesel engines in a narrow range of speed.

The same considerations listed for piston engines also apply to rotary combustion chamber engines. The benefit in reduction of CH emissions is of a much greater magnitude, however, due to the high rate of change in emission characteristics for rotary combustion engines with respect to engine speed.

The benefits to be derived from the application of this transmission to a gas turbine are also significant. Manufacturing cost is a major drawback in producing a turbine today. This, to a large degree, is a function of the complexity required in the design of a turbine for use under the varying torque and speed conditions of a road vehicle. With the hydromechanical transmission of this invention, the turbine can be programmed to operate only under those conditions during which it is most efficient. Therefore, a single-shaft turbine becomes feasible, as it is more economical to manufacture than the two-shaft design normally proposed for vehicle application. Since constant speed operation is feasible, the problems in connection with the throttle response time of a turbine do not arise. Because there is an infinite variation in speed and torque in the trans mission, and no interruption of power flow occurs at any time, the turbine is never unloaded.

SUMMARY OF THE INVENTION A family of transmission is provided, all having the same basic combination.

The power transmission includes in combination with input means and output means, two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, to provide an input member, an output member and a reaction member. The input member of one gear train is connected to the input means, and the input members of the two gear trains are interconnected so that both are driven by the input means. The reaction members of the two gear trains are interconnected, and their output members are separately clutchable to the output means. Speed varying means cause one output member to increase its speed and simultaneously cause the other side output member to decrease its speed, and vice versa, in a given range, for preparation for driving in the next range. The

3 speed varying means preferably comprises a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, one unit being connected in driving relation to the input means, and the other being connected in driving relation to the reaction members. The ratio of maximum speed of one output member to its minimum speed is the same as for the other output member, and is the same in each range. Thus each range, no matter how many are used, drives the output through an identical speed and torque ratio.

A feature of a preferred embodiment of this basic combination is a planetary assembly having two carriers, two sets of planet gears, two sun gears, and two ring gears. The two sun gears are mounted on the same reaction shaft. A first carrier serves as an input to the assembly, and the second carrier serves as one of two output members, the other one being the ring gear driven by the planets on the first carrier. The second ring gear serves as an input to the second part of the planetary assembly, and is splined to the first carrier. Clutches enable an output shaft to be clutched to either the second carrier or to the first ring gear, with an overlap where they are at the same speed.

The input shaft is clutchable. through a gear train, to the first carrier and it also drives a variable displacement hydraulic unit with hydraulically drives a fixed-displacement hydraulic unit, and this latter unit is connected by a gear train to the reaction shaft. Also, through clutch means, the hydraulic units are used in hydrostatic state for starting and for reverse operation.

The above combination gives a two-range hydromechanical operation, in addition to a hydrostatic start and reverse. A three-range hydromechanical operation can be achieved by adding a reduction planetary assembly beyond the main planetary assembly, with a third clutch serving to clutch one of the gears of the reduction assembly to a stationary housing. The reduction planetary assembly may be provided with two stages and two clutches to provide a four-range hydromechanical transmission in addition to the hydrostatic start and reverse.

The family of transmission of this invention uses a variable ratio hydromechanical assembly, which may go through its cycle of speed and torque variation two, three, or four times, depending on the required total torque multiplication range and the horsepower to be transmitted. The start and reverse ranges employ hydrostatic operation.

The cost reduction can be substantial by using the same variable assembly in many different applications. For example, the truck transmissions are shown as having three ranges, if approximately an 8:] total reduction range is required. Four ranges may be used if, with the same variable assembly, a reduction range of l6:1 is desired. Similarly, a two-range transmission, again using the same variable assembly, may be used for application where the speed variation range or the input horsepower need not be too great. Thus, it is possible to encompass a number of applications from farm tractors and construction equipment to highway and offhighway trucks using a large number of identical components.

The transmissions use the same variable planetary assembly, and differ only in whether there are range shifts beyond the output of the variable planetary, and, if so, how many. The range shifts occur at synchronized speeds, without interruption of power flow on either the upshift or the downshift. The starting and reverse ranges are hydrostatic and are not considered part of the working ranges. in most cases, the starting and reverse ranges operate at constant torque, rather than at constant horsepower, since maximum torque is limited by either maximum pressure or traction. The working ranges are considered those which operate at full and constant horsepower.

Hydromechanical transmissions have characteristics which are different from both gear boxes and torque converter transmissions. Since hydromechanical transmissions develop full static torque while at stall," the engine needs to develop only the horsepower necessary to make up the transmission losses. This is considerably less horsepower than that required to develop stall torque in a torque converter transmission.

However, since this horsepower is a dead loss, with the vehicle standing still, the amount of heat developed is greater than the average heat rejection requirement when operating in the full horsepower ranges. Therefore, one of three methods of protecting against excessive temperature rise must be used as described in the immediately following paragraphs.

a. Transmission may have such a wide ratio as to exceed the traction limit in torque requirement.

b. Controls may be provided to either unload the hydraulic system if torque capacity of the transmission has been exceeded or limit the engine input.

c. A large enough heat exchanger capacity has to be supplied.

The transmissions described all have a hydrostatic starting range in addition to the split power hydromechanical ranges; i.e., the four-range transmission has four split power ranges and a hydrostatic starting range. The ratio from top speed to bottom speed of a range and the number of ranges determine the hydraulic unit power requirement and the maximum hydraulic pressure for a given configuration. For any combination of vehicle gearing, weight and power, there exists an optimum transmission configuration which is capable of slipping the drive wheels without overpressuring the hydraulic units and which will allow delivery of full engine horsepower at speeds above the vehicle traction limit without exceeding the horsepower limitation of the hydraulic units.

in many applications, it may be more practical not to include the capability of slipping the tires at their maximum load. In this case, maximum transmission output torque may be limited by relief valve setting or by some other controls device. Also, hydraulic unit size can be reduced while not reducing transmission horsepower capacity.

The hydraulic unit requirement in the hydrostatic range is a function of vehicle speed at the beginning of the first split power range. For example, if the transmission can transmit only 50 percent of maximum engine power because of traction limitations, the hydraulic unit requirement in the hydrostatic range need be only 50 percent of the engine capability. Similarly, the maximum power which can be transmitted in the hydrostatic range for such a particular transmission may be full engine horsepower.

Although hydraulic requirements in the hydrostatic range decrease with decreasing shift point speed, the requirement in the split power ranges increases in proportion to the ratio per range. This is shown by the amount of hydraulic power transmitted in the hydromechanical ranges. Therefore, the initial shaft point speed and the ratio per range are chosen to optimize the maximum horsepower and pressure requirements in both the hydrostatic range and in the split power ranges.

In other words, a hydromechanical range of wider spread then required by torque multiplication at constant horsepower is used to reduce the hydraulic horsepower and pressure requirement in the hydrostatic range, at some expense of greater percentage of power transmitted hydraulically in the hydromechanical ranges.

A hydromechanical transmission is dependent on the hydraulic components for its torque multiplication, and therefore the engine is not required to operate at a torque rise in a reduced speeds. The engine may be operated at constant speed which could afford a savings by simplification of the engine fuel-governor system.

Other objects and advantages of the invention will appear from the following description of some preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a sectional view of a two-stage transmission embodying the principles of the invention, and transmission being partially spread out so that the meshing of two gears does not show.

FIG. 2 is a view in section along the line 22 in FIG. 1, (and also in FIG. 8) to show how the gears actually mesh.

FIG. 3 is a speed lines diagram, with output speeds in r.p.m. being plotted against the speeds of the planetary members in r.p.m. The clutches which are engaged in each range are identified.

FIG. 4 is a diagram with speed in r.p.m. being plotted against torque in thousands of inch-pounds.

FIG. 5 is a sectional view generally similar to FIG. 1 of a three-range transmission embodying the principles of the invention.

FIG. 6 is a speed lines diagram similar to FIG. 3 for the transmission of FIG. 5.

FIG. 7 is a speed torque diagram like FIG. 4, for the transmission of FIG. 5.

FIG. 8 is a sectional view similar to FIG. 1 of a fourrange transmission embodying the principles of the invention.

FIG. 9 is a speed lines diagram like FIG. 3 for the transmission of FIG. 8.

FIG. 10 is a torque-speed diagram like FIG. 4 for the transmission of FIG. 8.

FIG. 11 is a diagrammatic view of another modified form of two-range transmission embodying the principles of the invention.

FIG. 12 is a diagrammatic view of another modified form of two-range transmission embodying the principles of the invention.

FIG. 13 is a view in section taken along the line 13-13 in FIG. 12.

FIG. 14 is a speed lines diagram similar to FIG. 3 for the transmission of FIGS. 12 and 13.

FIG. 15 is a diagrammatic view of a modified threerange transmission embodying the principles of the invention.

FIG. 16 is a speed lines diagram somewhat similar to FIG. 6 for the transmission of FIG. 15.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A Two-Range Transmission (FIGS. 1-4) An input shaft 20 carries an input gear 21 which meshes with a gear 2 on a shaft 23. The shaft 23 drives a variable displacement hydraulic unit 24 and is also connected to one portion ofa clutch 25. The other portion of the clutch 25 is integral with a gear 26, which has a hub 27. The gear 26 drives a gear 28, which is, operationally, at least, a part of a first planetary carrier 30 that is the input member of a variable speed planetary assembly.

The carrier 30 carries on pins 31 a set of planet gears 32, which mesh with both a first sun gear 33 and a first ring gear 34. The carrier 30 continues on to form spline teeth 35 which mesh with a second ring gear 36, which rotates at the same speed as and together with the carrier 30 and the gear 28, and this second ring gear 36 is the input into the secondary part of the variable speed planetary assembly.

The secondary part of the planetary assembly includes a second carrier 37 which carries pins 38 on which are mounted planet gears 40. These planet gears 40 mesh with the ring gear 36 and also with a second sun gear 41, which is integral with or securely in driving connection with a shaft 42, as is the gear 33, which meshes with the planetary pinions 32 of the first part of the planetary assembly. Thus these two sun gears 33 and 41, which are reaction gears, rotate at the same speed and are really one member except for constructional reasons, while the two inputs which are the carrier 30 and the second ring gear 36 are also really one member except for constructional reasons, and they rotate at the same speed.

This unusual planetary assembly has the advantages I) that there are very low gear loadings, (2) that there are very low bearing loadings, (3) that the pinions 32 and 40 do not have to intermesh, (4) that it is much easier to construct than a compound planetary (5) that it is susceptible to simple construction in the reaction members 33 and 41, since they both turn at the same speed and are connected to the common shaft 42, (6) the rotational speeds of the planets do not exceed allowable limits, and (7) and than three planets can be used in each planetary assembly to afford greater power capacity.

This reaction shaft 42 carries gear 43, which is a reaction gear meshing with a gear 44 on a shaft 45 that is connected to a fixed-stroke hydraulic unit 46. The shaft 45 also carries a gear 47 which is meshed with a gear 48 which is clutchable to the shaft 23 by a clutch 49.

The hydraulic unit 24 is variable in stroke and runs at constant speed, driven at all times by the input shaft 20 through the gears 21 and 22 and the shaft 23. The unit 24 is fully variable in stroke in either direction from zero, so that it is capable of reverse operation. The hydraulic unit 46, which is connected to the reaction gears 33 and 41 through the shaft 42, gears 43 and 44 and shaft 45, is fixed in stroke and therefore an over-center operation of the wobble plate of the hydraulic unit 24 results in a change between a forward and a backward rotation of the hydraulic unit 46.

The members of the planetary assembly are driven in a direction depending on the stroking of the hydraulic unit 24,

The plaaetary assembly drives an output shaft 50 through either of two output members, the ring gear 34 and the carrier 37, which may be secured to a shaft 51, all of the shafts 50, 51, 42, and 20 preferably being coaxial, or axially in line with each other. The shaft 51 is connected to the output shaft 50 by clutch 52, and the ring gear 34 is connected to a tubular member 53 on the output shaft by a clutch 54. Shift is made between the clutches 52 and 54 when their speeds are synchronous, with a slight overlap, the clutch 52 driving the output shaft 50 in one range of speed and the clutch 54 driving the output shaft in the other range of speed.

The clutch 49, which connects the gear 48 with the shaft 23 is used for starting and is engaged normally only when the transmission is starting, going either in forward or reverse. At this time, the clutch 25 is disengaged, and the operation is purely hydrostatic. Thus, the input shaft 20 drives the gear 21 which drives the gear 22 to drive the shaft 23 and thus the variable stroke hydraulic unit 24. The unit 24 supplies oil to the fixed-stroke hydraulic unit 46 by means of oil lines 55 and 56, and the hydraulic unit drives the planetary members through the gears 47 and 48, the clutch 49, and the gears 26 and 28, the gear 26 at that time being disconnected from the input shaft due to the disengagement of the clutch 25.

In the speed-lines diagram, FIG. 3, various lines have been labeled with the numbers of the gears or shafts of FIG. 1, whose speeds they represent. Thus, the input gear 21 runs at a constant speed, and the broken line at the left end of the hydrostatic range forward indicates that it is not at that time connected to the plane tary assembly, because the clutch 25 is than disengaged. Instead, as shown, the clutch 49 is then engaged, and the clutch 52 is also engaged to drive the output shaft 50. During engagement of the clutch 49 the planetary assembly simply acts as a gear reduction train driven by the hydraulic unit 46, which in turn is driven from the input shaft 20 through the gears 21 and 22 and the hydraulic unit 24. Starting from zero stroke of the hydraulic unit 24 at zero speed, stroking it in one direction causes the output shaft 50 to go in reverse and stroking it in the opposite direction causes the output shaft 50 to go forward.

Assuming that the output shaft 50 is going forward, the carrier 37 will be increasing in speed up to the point where it reaches the end of the hydrostatic forward range, i.e., the highest speed in that range. Simultaneously the sun or reaction gears 33 and 41, and therefore the shaft 42 and the gear 43, reach a certain maximum negative speed. The ratios of the gears 43, 44 and 47, 48 are such that at that point it becomes possible to engage the clutch 25 synchronously and, immediately thereafter, to disengage the clutch 49, the ratio between the gears 26 and 28 and the ratio between the gears 21 and 22 being such that at this speed the gear 28 can be connected to the input gear 21. In this case, the ratio is two to one. Thereafter, the gear 26 serves as input into the planetary assembly, and from this time on the transmission is in the hydromechanical state, because the power is transmitted from the input shaft 20 through the gears 21 and 22, the clutch 25 and the gears 26 and 28 and thereafter is delivered through two channels, one hydrostatic and the other mechanical, to the output shaft 50 in a manner which splits the power between the hydraulic and the mechanical power, as is shown in the diagrams, FIG. 4.

At the time of shifting from the hydrostatic range to the first hydromechanical range all the members 28, 33, 34 and 41 are running at different speeds, and the members 33 and 41 are running in a direction opposite to that of the member 34. Therefore, an idler arrangement must be interposed between some of these members in order to adjust their speeds and ratios to conditions such that a clutch may be engaged. This idler arrangement is provided by the gears 47 and 48, which produce the right sense of direction between the gear 43, which is made integral with the gears 41 and 33, and the gear 26, which drives the member 28. Consequently, when clutch 25 is engaged at the point where the hydrostatic range ends and hydromechanical Range l begins, from that point the members 34, 28, 33, 41 and 27 all converge to zero speed.

As the transmission proceeds in Range I of this hydromechanical state, which it has just entered, it will be noted that the speeds of all the planetary members, which converged at starting at one synchronous point A, again converge at one synchronous point B where the operation is shifted from Range 1 to Range II by engaging the clutch 54 and disengaging the clutch 52. The operation for Range l consists of one planetary member, the carrier 37, increasing its speed, while another planetary member, the ring gear 34, is decreasing its speed, and that the ratios between the maximum and minimum speeds for each of the members 37 and 34 are identical, for example, two to one. The function of increasing one planetary member through a given ratio while at the same time decreasing the other planetary member through the same ratio without driving any thing until it reaches a synchronous point with the first member and can thereafter accept the drive, this function is a vital point of this hydrostatic transmission and this equality of ranges is novel. Furthermore, this equality of ranges can extend over more than the two ranges shown in this embodiment, in fact it can extend over any number of ranges. When this equality of speeds is reached at the end of Range 1, the members carrying the clutches 52 and 54 are synchronous, and therefore a shift can be made from the clutch 52 to the clutch 54 with a desirable overlap to avoid loss of power transmission but without any significant relative speed of the clutch members. After this shift is made, the clutch S4 continues to transmit power from the ring gear 34 to the output shaft 50, reaching its maximum speed at the end of Range ll.

While all these speed relations are taking place, there are interesting relations between the horsepower that is transmitted hydrostatically and that which is transmitted mechanically, and these relations are illustrated in FIG. 4. The amounts of torque and horsepower developed by the output of the transmission are shown, a line HP showing the input horsepower and line TQ showing the output torque. Starting from zero speed, the input horsepower HP increases to a maximum at the end of hydrostatic range. Thereafter the input horsepower HP proceeds at a constant value, whereas the torque TQ is first a constant over the hydrostatic range and thereafter decreases as the speed increases, a necessary condition to be met transmitting constant horsepower over a variation of speed, since torque multiplied by speed is a constant in the constant horsepower range. The shaded areas in FIG. 4 represent the hydraulic horsepower, and in the area C in the hydrostatic range, all the horsepower is hydrostatic. 

1. A power transmission comprising input means, output means, a planetary assembly having an input member, two coaxial output members, and reaction means, and having two separate and distinct sets of planet gears, each set being mounted on separate and distinct rotatable carriers, means for alternately and separately connecting each of said output members to said output means, and speed-varying means for causing one said output member to increase its speed and for simultaneously causing the other said output member to decrease its speed and vice versa.
 2. A power transmission comprising input means, output means, a planetary assembly having an input member, two coaxial output members, and reaction means, and having two separate and distinct sets of planet gears, each set being mounted on a separate and distinct rotatable carrier, and speed-varying means for causing one said output member to increase its speed and for simultaneously causing the other said output member to decrease its speed and vice versa, said speed-varying means comprising a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, a first said unit being connected in driving relation to said input means, a second said unit being connected in driving relation to said reaction means.
 3. A power transmission according to claim 2, wherein said first unit is variable in stroke and runs during operation at constant speed while said second unit is fixed in stroke and variable in speed.
 4. A power transmission comprising input means, output means, a planetary assembly having an input member, two coaxial output members, and reaction means, speed-varying means for causing one said output member to increase its speed and for simultaneously causing the other said output member to decrease its speed and vice versa, said planetary assembly comprising two planetary gear trains, each having its own input member, output member and reaction member, the input member of a first said gear train being connected to said iNput means, the input members of the two said gear trains being connected together so that both are driven by said input means, said reaction members of said two gear trains being interconnected, and said coaxial output members being separately clutchable to said output means, and clutch means for engaging and disengaging said input means with and from said input member of said first gear train.
 5. A power transmission according to claim 4, wherein a drive gear is always engaged with said input member of said first gear train, and said clutch means engages and disengages said drive gear with and from said input means.
 6. A power transmission according to claim 5 having additional clutch means for engaging said drive gear with said reaction members and for disengaging it therefrom.
 7. A power transmission according to claim 6 having idler means, said drive gear being connected to said reaction members when said additional clutch means is engaged through said idler means.
 8. A power transmission according to claim 5 having a reaction shaft carrying both said reaction members, and additional clutch means causing direct engagement of said input member of said first gear train with said reaction shaft.
 9. A power transmission according to claim 4 wherein said two planetary gear trains are identical, each having identical input members, identical output members, and identical reaction members.
 10. A power transmission according to claim 9 wherein said identical reaction members comprise a single elongated gear having portions for each said planetary gear train.
 11. A transmission, comprising a planetary assembly having a single input means, two coaxial output means, and a single reaction means, and having two separate and distinct sets of planet gears, each set being mounted on a separate and distinct rotatable carrier, and two hydraulic pump-motors connected to each other, one serving as a pump while the other serves as a motor, and vice versa, one said pump-motor being connected to said input means and the other to said reaction means, said pump-motors serving as means for varying the speed of said two output means so that one increases in speed while the other decreases in speed and vice versa.
 12. The transmission of claim 11 wherein said single reaction means is coaxial with said two coaxial output means.
 13. A transmission comprising a planetary assembly having, all coaxial with each other, a single input means, two output means, and a single reaction means, and having two separate and distinct sets of planet gears, each set being mounted on a separate and distinct rotatable carrier, two hydraulic pump-motors connected to each other, one serving as a pump while the other serves as a motor, and vice versa, one said pump-motor being connected to said input means and the other to said reaction means, said pump-motors serving as means for varying the speed of said two output means so that one increases in speed while the other decreases in speed and vice versa.
 14. A transmission, comprising a planetary assembly having a single input means, two output means, and a single reaction means, and having two separate and distinct sets of planet gears, each set being mounted on a separate and distinct rotatable carrier, an output shaft, clutch means directly connecting said output members to said output shaft, and two hydraulic pump-motors connected to each other, one serving as a pump while the other serves as a motor, and vice versa, one said pump-motor being connected to said input means and the other to said reaction means, said pump-motors serving as means for varying the speed of said two output means so that one increases in speed while the other decreases in speed and vice versa.
 15. A power transmission, including in combination: input means, output means, two planetary gear trains each having its own input member, output member and reaction member, thE input member of a first said gear train being connected to said input means, the input members of the two gear trains connected together so that both are driven by said input means, the reaction members of the two gear trains being interconnected, and their output members being coaxial and separately clutchable to said output, means and speed varying means for causing one said output member to increase its speed and for simultaneously causing the other said output to decrease its speed, and vice versa.
 16. The power transmission of claim 15 wherein said speed varying means comprises: a pair of hydraulic units hydraulicallly interconnected so that one serves as a pump while the other serves as a motor and vice versa, a first said unit being connected in driving relation to said input means, a second said unit being connected in driving relation to said reaction members, said first unit being variable in stroke and running during operation at constant speed while said second unit is fixed in stroke and variable in speed.
 17. The power transmission of claim 16 having a drive gear always engaged with said input member of said first gear train, clutch means for engaging and disengaging said input means with and from said drive gear, idler means in driving relation with said second unit, additional clutch means for engaging said drive gear, through said idler means, with said reaction members and for disengaging it therefrom.
 18. The power transmission of claim 15 wherein at least one said output member is clutchable to said output means through a reduction gear train.
 19. The power transmission of claim 18 wherein both said output members are clutchable to said output means through separate reduction gear trains.
 20. The power transmission of claim 15 wherein both said output members are clutchable directly to said output means.
 21. A power transmission, including in combination: input means, output means, two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, to provide an input member, an output member and a reaction member, the input of a first said gear train being its carrier and being connected to said input means, the input member of a second gear train being its ring gear and being drivingly connected to the carrier of said first gear train, so that both are driven by said input means, the reaction members of the two gear trains being the sun gears mounted on a common reaction shaft, the output members of the two gear trains being coaxial and separately clutchable to said output means, and speed varying means for causing one said output member to increase its speed and for simultaneously causing the other said output member to decrease its speed, and vice versa.
 22. The power transmission of claim 21 wherein the output member of said first gear train is its ring gear.
 23. A power transmission, including in combination: input means, output means, two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, to provide an input member, an output member and a reaction member, the input member of a first said gear train being its carrier and being connected to said input means, the input member of a second said gear train being its ring gear and being drivingly connected to the carrier of said first gear train, so that both are driven by said input means, the reaction members of the two gear trains being the sun gears mounted on a common reaction shaft, the output members of the two gear trains being coaxial and separately clutchable to said output means, speed varying means for causing one said output member to increase its speed and for simultaneously causing the other said output member to decrease its speed, and vice versa, a stationary causing, a reduction planetary assembly having a sun gear, a ring gear, and planet gears and a carrier secuRed to said output means, driving connection means connecting said ring gear of said first gear train to the sun gear of said reduction planetary assembly, first clutch means for connecting said ring gear of said first gear train to said carrier of said reduction planetary assembly, and first brake means for connecting said ring gear of said reduction planetary assembly to said stationary casing, to hold that ring gear stationary.
 24. The power transmission of claim 23 wherein the output member of said second gear train is its carrier having integral therewith an extension shaft aligned with said reaction shaft.
 25. The power transmission of claim 24 having in addition: a second reduction planetary assembly having the same carrier as the first-mentioned said reduction planetary assembly and having a sun gear mounted on and in driving relation with said extension shaft, planet gears, and a ring gear, second clutch means for coupling said extension shaft to said output means, and second brake means for coupling said ring gear of said second reduction planetary assembly to said stationary casing.
 26. A power transmission, including in combination: input means, output means, two planetary gear trains both coaxially aligned with said output means and each having its own input member, output member, and reaction member, the input member of a first said gear train being connected to said input means and to the input member of the second said gear train, so that both said gear trains are driven by said input means, the reaction members of the two gear trains being secured to a common reaction shaft, clutch means for separately clutching said output members to said output means, and speed varying means for causing one said output member to increase its speed while simultaneously causing the other said output member to decrease its speed and vice versa.
 27. The power transmission of claim 26 wherein said speed varying means comprises: a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, a first said unit being connected in driving relation to said input means, a second said unit being connected in driving relation to said reaction shaft, said first unit being variable in stroke and running during operation at constant speed while said second unit is fixed in stroke and variable in speed, and said input means comprises: an input shaft having a first gear thereon, an auxiliary shaft having a second gear thereon meshed with said first gear, said shaft driving said first unit, a third gear mounted rotatably on said auxiliary shaft and engaging the input means of said first gear train, and clutch means for engaging and disengaging said thrid gear with and from said auxiliary shaft.
 28. The power transmission of claim 27 wherein said third gear has an extension, said second unit has a shaft with fourth and fifth gears secured thereto, a sixth gear secured to said reaction shaft and meshed with said fourth gear, a seventh gear meshed with said fifth gear, and additional clutch means for engaging said extension of said third gear with said seventh gear and for disengaging it therefrom.
 29. The power transmission of claim 27 having additional clutch means for causing direct engagement of said input member of said first gear train with said reaction shaft.
 30. In a power transmission having input means and output means, the combination therewith of: two planetary gear trains each having its own carrier and its own planet, sun, and ring gears, to provide an input member, an output member and a reaction member, the input member of a first said gear train being its carrier and being connectable to said input means, the input member of a second said gear train being its ring gear and being connected by gear coupling to the carrier of said first gear tRain, so that both are driven by said input means, the reaction members of the two gear trains being the sun gears mounted on a common reaction shaft, the output members of the two gear trains being separately clutchable to said output means, the output member of said first gear train being its ring gear, a stationary casing, a reduction planetary assembly having a sun gear, a ring gear, and planet gears and a carrier secured to said output means, driving connection means connecting said ring gear, a ring gear, and planet gears and a carrier secured to said output means, driving connection means connecting said ring gear of said first gear train to the sun gear of said reduction planetary assembly, first clutch means for connecting said carrier of said second gear train to said carrier of said reduction planetary assembly, and first brake means for connecting said ring gear of said reduction planetary assembly to said stationary casing, to hold that ring gear stationary, said reduction planetary assembly and said first and second planetary assemblies all being identical to each other as to the sizes and teeth of their gears and carriers, and speed varying means comprising a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, a first said unit being connected in driving relation to said input means and being variable in stroke and set to run at a constant speed, a second said unit being connected in driving relation to said common reaction shaft and being fixed in stroke and variable in speed in both directions, a shaft on which said second unit is mounted, a third hydraulic unit clutchable to said last-named shaft and connected to said first hydraulic units for use along with said second unit, said third unit being variable in stroke.
 31. A hydromechanical transmission, including in combination a planetary assembly having a first sun gear serving as a reaction member, a first ring gear serving as a first output member, a first planet carrier serving as the input member and carrying a first set of planet gears meshed with both said first sun gear and said first ring gear, a second sun gear serving as a reaction member, a second ring gear serving as an input member, and splined to said first planet carrier, a second planet carrier serving as a second output member and carrying a second set of planet gears meshed with both said second sun gear and said second ring gear, a common reaction shaft to which both said first and second sun gears are secured, an input shaft, drive transmitting means for connecting and disconnecting said input shaft with said first planet carrier, an output shaft, a pair of synchronous clutch means for connecting, during a first hydromechanical speed range, said second planet carrier to said output shaft and, during a second hydromechanical speed range, said first ring gear to said output shaft, with over lap at the shift point between said first and second speed ranges, a variable-displacement hydraulic unit driven mechanically by said input shaft, a fixed-displacement hydraulic unit, driven hydraulically by said variable-displacement hydraulic unit and having an auxiliary shaft, and gear means connecting said auxiliary shaft of said fixed-displacement hydraulic unit to said reaction shaft.
 32. A hydromechanical transmission, including in combination: a planetary assembly having a first sun gear serving as a reaction member, a first ring gear serving as a first output member, a first planet carrier serving as the input member and carrying a first set of planet gears meshed with both said first sun gear and said first ring gear, a second sun gear serving as a reaction member, a second ring gear serving as in input member, and splined to said first planet carrier, a second planet carrier serving as a second output member and carrying a second set of planet gears meshed with both said second sun gear and said second ring gear, a common reaction shaft to which both said first and second sun gears are secured, an input shaft, drive transmitting means for connecting said input shaft to and disconnecting it from said first planet carrier, an output shaft, a pair of synchronous clutch means for connecting, during a first hydromechanical speed range, said second planet carrier to said output shaft and, during a second hydromechanical speed range, said first ring gear to said output shaft, with overlap at the shift point between said first and second speed ranges a variable-displacement hydraulic unit driven mechanically by said input shaft, a fixed-displacement hydraulic unit, driven hydraulically by said variable-displacement hydraulic unit and having an auxiliary shaft, gear means connecting said auxiliary shaft of said fixed-displacement hydraulic unit to said reaction shaft, a stationary housing, a reduction planetary train having a third carrier locked to said output shaft, a third set of planet gears, a third sun gear having an auxiliary gear meshed to said first ring gear, a third ring gear, and brake means for connecting said third ring gear to said stationary housing.
 33. The hydromechanical transmission of claim 32 having hydrostatic start and reverse means, comprising: a drive gear in said drive transmitting means, driving said first planet carrier, a first clutch for placing said drive gear in driving relation with said input shaft and for releasing it therefrom, and a second clutch for placing said reaction shaft in driving relation with said first planet carrier.
 34. The hydromechanical transmission of claim 32 wherein said reduction planetary train has a fourth set of planet gears, a fourth sun gear lock to said second planet carrier, and a fourth ring gear, and means for locking said fourth ring gear to said stationary housing.
 35. The hydromechanical transmission of claim 31 having hydrostatic start and reverse means comprising: a drive gear in said drive transmitting means driving said first planet carrier, a first clutch for placing said drive gear in driving relation with said input shaft and for releasing it therefrom, said drive gear having an extension, an idler gear around said extension, and meshed to gear means on said auxiliary shaft, and a second clutch for connecting said idler gear to the extension of said drive gear.
 36. The hydromechanical transmission of claim 31 wherein said planetary assembly and said output and reaction shafts are coaxial.
 37. The hydromechanical transmission of claim 36 wherein said input and output shafts are coaxial.
 38. A hydromechanical transmission, including in combination: a driving shaft, a first intermediate shaft coaxial with said driving shaft, a second intermediate shaft coaxial with said first intermediate shaft, an output shaft coaxial with said second intermediate shaft, first clutch means for releasably clutching said driving shaft to said first intermediate shaft, second clutch means for releasably clutching said first intermediate shaft to said second intermediate shaft, third clutch means for releasably clutching said second intermediate shaft to said output shaft, a stationary casing, a first planetary gear assembly having a first sun gear mounted on said first intermediate shaft, a first ring gear secured to said casing, a first planet carrier and a first set of planet gears in mesh with said first sun gear and with said first ring gear, a first hollow shaft concentric with a portion of said second intermediate shaft and drivingly connected to said first carrier, a second planetary gear assembly having a second sun gear secured to said second intermediate shaft, a second planet carrier secured to said first hollow shaft, seCond and third sets of planet gears carried by said carrier with each gear of said second in mesh with a gear of said third set, said second set of planet gears being in mesh with said second sun gear, and a third sun gear in mesh with said third set of planet gears, a second hollow shaft concentric with said first hollow shaft and secured to said third sun gear, a third planetary assembly having a fourth sun gear mounted on and secured to said second hollow shaft, a second ring gear secured to said second planet carrier, a third planet carrier, and a fourth set of planet gears in mesh with said fourth sun gear and said second ring gear, fourth clutch means for releasably clutching said third planet carrier to said output shaft, and speed-varying means for causing said second intermediate shaft to increase its speed and for simultaneously causing said third planet carrier to decrease its speed and vice versa.
 39. The transmission of claim 38 wherein said speed-varying means comprises a pair of hydraulic units hydraulically interconnected so that one serves as a pump while the other serves as a motor and vice versa, a first said unit being connected in driving relation with said driving shaft, a second said unit being connected in driving relation with said second hollow shaft.
 40. The transmission of claim 39 wherein said first unit is variable in stroke and runs during operation at a constant speed while said second unit is fixed in stroke and variable in speed.
 41. The transmission of claim 39 having a first gear secured to said driving shaft, a second gear in driving relation with said first unit and in mesh with said first gear, a third gear secured to said second hollow shaft, and a fourth gear in driving relation with said second unit and in mesh with said third gear.
 42. A hydromechanical transmission, including in combination a planetary assembly having a first sun gear serving as a reaction member, a first ring gear serving as a first output member, a first planet carrier serving as the input member and carrying a first set of planet gears meshed with both said first sun gear and said first ring gear, a second sun gear serving as a reaction member, a second ring gear serving as an input member, and splined to said first planet carrier. a second planet carrier serving as a second output member and carrying a second set of planet gears meshed with both said second sun gear and said second ring gear, a common reaction shaft to which both said first and second sun gears are secured, an input shaft, clutching means for connecting said input shaft to said first planet carrier, an output shaft, a pair of synchronous clutch means for connecting, during a first hydromechanical speed range, said second planet carrier to said output shaft and, during a second hydromechanical speed range, said first ring gear to said output shaft, with over lap at the shift point between said first and second speed ranges, a variable-displacement hydraulic unit driven mechanically by said input shaft, a fixed-displacement hydraulic unit, driven hydraulically by said variable-displacement hydraulic unit and having an auxiliary shaft, and gear means for connecting said auxiliary shaft of said fixed-displacement hydraulic unit to said reaction shaft.
 43. The hydromechanical transmission of claim 42 wherein the said first and second sun gears are identical, said first and second ring gears are identical, said first and second planet carriers are identical, and said first and second sets of planet gears are identical.
 44. The hydromechanical transmission of claim 43 wherein said first and second sun gears are part of a single elongated gear.
 45. A hydromechanical transmission, including in combination a first planetary assembly having a first sun gear serving as a reaction member, a first ring gear serving as a first output member, a first planet carrier servIng as the input member and carrying a first set of planet gears meshed with both said first sun gear and said first ring gear, a second sun gear serving as a reaction member, a second ring gear serving as an input member, and splined to said first planet carrier, a second planet carrier serving as a second output member and carrying a second set of planet gears meshed with both said second sun gear and said second ring gear, a common reaction shaft to which both said first and second sun gears are secured, a second planetary assembly having a third sun gear serving as an input member and connected to said first ring gear, a third ring gear serving as a reaction member, a third planet carrier serving as a third output member and carrying a third set of planet gears meshed with both said sun gear and said third ring gear, a stationary housing, an input shaft, clutching means for connecting said input shaft to said first planet carrier, an output shaft connected to said third planet carrier, a pair of synchronous clutch means for connecting, during a first hydromechanical speed range, said third ring gear to said stationary housing, and, during a second hydromechanical speed range, said second planet carrier to said third planet carrier and thereby to said output shaft, with over lap at the shift point between said first and second speed ranges, a variable-displacement hydraulic unit driven mechanically by said input shaft, a fixed-displacement hydraulic unit, driven hydraulically by said variable-displacement hydraulic unit and having an auxiliary shaft, and gear means connecting said auxiliary shaft of said fixed-displacement hydraulic unit to said reaction shaft.
 46. The hydromechanical transmission of claim 45 wherein the said first and second sun gears are identical, said first and second ring gears are identical, and said first and second sets of planet gears are identical.
 47. The hydromechanical transmission of claim 46 wherein said first and second sun gears are part of a single elongated gear.
 48. The hydromechanical transmission of claim 45 wherein said first, second and third sun gears are identical, said first, second, and third ring gears are identical, and said first, second, and third sets of planet gears are identical.
 49. The hydromechanical transmission of claim 48 wherein there is a third hydraulic unit, variable in displacement, hydraulically connected to said earlier-named variable-displacement hydraulic unit, and means for clutching said third unit to said auxiliary shaft of said fixed-displacement hydraulic unit. 